As a new addition to the Diagnostic and Statistical Manual-5 (DSM-5), Hoarding Disorder (HD) is defined by persistent difficulty parting with possessions due to distress associated with discarding, urges to save, and/or difficulty making decisions about what to keep or dispose of. Clutter accumulates and fills living areas to prevent normal use of space, resulting in distress and/or disability. Hoarding symptoms cause significant impairment, increased medical problems, and poor quality of life for our Veterans, particularly our older Veterans. Providers treat Veterans for other medical or psychiatric complaints yet frequently miss an important source of disability and burden on our system. This insidious condition is costly to the VA system as patients continue to decompensate and need greater amounts of care over the lifespan. Given that over 6% of the population has HD, a higher proportion than are diagnosed with schizophrenia or bipolar disorder, further research on the mechanism and efficacy of an appropriate treatment is desperately needed. Current behavioral intervention methods for HD range from ineffective to relatively small gains. Case management is typically used to treat HD, which produces inadequate outcomes and clients resurface in systems of care. Cognitive-behavioral therapy (CBT) for HD includes multiple components (assessment: 2-3 sessions, case formulation: 2 sessions, skills training: 2-3 sessions, combined exposure and cognitive therapy: 15-20 sessions, and motivational interviewing: throughout) and yields poor responses rates (i.e. <20% symptom reduction) in older adults. Outcomes in midlife HD patients are not much better, with symptom reduction rates ranging from 14-29% in HD symptoms following a lengthy course (4-9 months) of CBT for HD. Executive dysfunction (ED) is linked to both HD symptom severity and poor outcomes of CBT for HD. Decision making, categorization, problem solving, inhibition, planning, organization, and cognitive flexibility difficulties are evident in HD patients across th lifespan, particularly in older patients. The VA has funded the development of an integrated behavioral treatment (Cognitive Rehabilitation and Exposure/Sorting Therapy; CREST) that targets both neurocognitive functioning and the core symptoms of HD (VA Career Development Award; Ayers PI). This treatment includes Compensatory Cognitive Training (CCT) to improve executive functioning and is combined with exposure therapy (ET) that targets avoidance of discarding/not acquiring. Preliminary results suggest that CREST is a highly feasible and acceptable treatment that doubles outcome rates compared to CBT for HD. Our proposed study will further develop this innovative intervention while testing whether it works through the mechanisms it targets and examining outcome moderators that may identify which patients are more likely to benefit. We propose to conduct a randomized controlled trial comparing six months (26 sessions) of CREST to six months of ET alone, in 136 participants with HD. Assessments will be administered at baseline, during treatment (sessions 7, 13, 21), post-treatment, and 3 and 6-month follow-up. The primary objective is to evaluate whether CREST significantly reduces hoarding symptoms and improves functional capacity and quality of life when compared to exposure therapy alone. We will also examine the impact of treatment mediators; treatment adherence, changes in executive functioning, avoidance, and symptom severity on outcomes. Age and executive functioning will also be explored as potential moderators. Finally, by repeatedly measuring treatment targets, we will examine time to maximum treatment effect. By providing a treatment for many Veterans with HD, we can alter the course of their symptom trajectory and negative consequences, resulting in both reduced burden on the healthcare system and improved quality of life for Veterans.